Joseph, re-reading your initial post, something is puzzling me:

“Ted Gioia, who is primarily known for his books about jazz, wrote in his 2009 blues book, ‘the Delta's claim as [the blues'] birthplace is as strong as any other region's.’ Oh, is it, if Emmet Kennedy, Willie Cornish, and Antonio Maggio all said they had (independently) encountered three blues tunes in Louisiana before 1908?”

Why single out these three examples from Louisiana, when you seem to consider blues at least as many pieces of evidence in the Delta from around the exact same time, or sometimes maybe earlier, like “Handy / Tutwiler,” “Handy / Cleveland,” and “Gus Cannon / “Poor Boy” / Alec Lee,” for example?

And besides the (not self-evident) argument that three accounts from three witnesses for one given place are more compelling than one, do you feel there is a reason to prefer these Louisiana examples to contemporary or sometimes far earlier accounts, in Indiana, Alabama, Tennessee etc, which, again, you seem to consider blues?